Guide · Financial Calculator
How to calculate your mortgage payment
A mortgage is one of the most straightforward Time Value of Money problems. You borrow a fixed amount today (PV), repay it in equal monthly instalments (PMT) over a set number of years (N), at a fixed interest rate (I/Y). Pebble's Financial calculator lets you solve for any one of these variables in seconds.
The five TVM variables
Switch Pebble to Financial mode (tap the mode button and select 💰). You'll see five fields — here's what each means for a mortgage:
- N — Total number of monthly payments (years × 12)
- I/Y — Annual interest rate as a percentage (e.g. 6.75)
- PV — Loan amount (the amount you're borrowing)
- PMT — Monthly payment (what you want to find)
- FV — Remaining balance at the end — enter 0 for a fully paid-off mortgage
Example: 30-year mortgage
You're buying a $400,000 home with a 20% down payment ($80,000), so your loan amount is $320,000. Your lender is offering 6.75% annual interest on a 30-year term. What is your monthly payment?
Enter these values, then tap CPT → PMT
Over 30 years you'll pay roughly $747,000 in total — meaning about $427,000 goes to interest. That's a useful number to have in mind when comparing loan options.
Example: 15-year mortgage (same loan)
Same $320,000 loan at 6.75%, but over 15 years instead. How much more do you pay per month, and how much interest do you save overall?
Enter these values, then tap CPT → PMT
The 15-year payment is about $756 more per month — but your total interest paid drops to around $190,000, saving you over $237,000 compared to the 30-year term. The financial calculator makes this comparison instant.
Solving for other variables
The financial calculator isn't just for finding PMT. If you already know what monthly payment you can afford, enter it as PMT and tap CPT → PV to find the maximum loan you qualify for. Or enter a target payoff timeline and solve for I/Y to see what interest rate you need to negotiate.